Oral-History:Henry Oman

About Henry Oman

Henry Oman

Henry Oman worked with Allis Chalmers on the propulsion machinery for submarines and Destroyer Escorts during the war, received a Master’s degree at Oregon State University while working at Boeing on the changing of the fusible resistance link point-by-point as it approached melting temperatures, limiters, and did graduate work at Illinois Tech. He was fundamental in establishing the Power Electronics Society, which has been responsible for the power electronics now all over airplanes. This society grew out of Oman’s initiative to form a conference to discuss the creation of an inverter that would make a.c. out of d.c. with solid-state parts. He also played a role in forming the Intersociety Energy Conversion Engineering Conference. Oman also worked on B-52 bombers and atomic-powered airplane, the Rail Garrison Peacekeeper, tested electromagnetic radiation emitted from transmission lines, was the secretary of the Engineering Society of Milwaukee and editor of Milwaukee Engineering, wrote for the Advanced Battery Technology magazine, and worked on battery-powered electric bicycles. He was awarded the Harry Mimmo Award by the IEEE Aerospace and Electronic Systems magazine on the topic of the energy cost of traveling 1,000 miles comparing everything from the Queen Mary steamship to walking. Oman also worked on solar panels for spacecraft and solar power satellites. In this interview, he furthermore provides details of the major advance in aerospace electronics and aerospace power systems and the challenges to be faced in the upcoming decades.

About the Interview

HENRY OMAN: An Interview Conducted by David Hochfelder, IEEE History Center, 17 December 1999

Interview # 386 for the IEEE History Center, The Institute of Electrical and Electronics Engineers, Inc.

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It is recommended that this oral history be cited as follows:

Henry Oman, an oral history conducted in 1999 by David Hochfelder, IEEE History Center, Hoboken, NJ, USA.

Interview

Interview: Henry Oman

Interviewer: David Hochfelder

Date: 17 December 1999

Place: Normandy Park, Washington

Advances in aerospace electronics and aerospace power systems

Hochfelder:

Good afternoon. Thanks for agreeing to do this interview.

Oman:

It’s a pleasure.

Hochfelder:

Would you explain some of the major advances in aerospace electronics and aerospace power systems in the past fifty years?

Fifty years ago airplanes had power systems which were derived from automobiles and trucks. The earliest airplanes had 12-volt power supplies, but then the loads became so great that they had to go to 24-volt batteries. A 24-volt generator actually delivered 28 volts to charge the battery. If an airplane lost its engine, its electronics could still run with battery power. As airplane loads grew the generated current grew proportionally. By World War II B-29 bombers carried huge cables that conducted its 28-volt power. The cables in the airplanes had to be redundant and fused at each end. If one cable were grounded or shorted by gunfire, it would be isolated by the melting of the fuses on each end. The airplane would continue to have power carried by the redundant cables. As a consequence the cable weight in an airplane became very substantial and it had to be hauled for the life of the airplane.

The next approach that we worked on at the time I joined Boeing was a higher voltage. We figured that because Edison had liked 120 volts, why not make the airplane’s system run on 120 volts? The evaluation of a 120-volt system was assigned to the Boeing Acoustics Electrical Laboratory. The chief of the laboratory decided that this was something we must develop. He bought some old army tank engines and we had a contractor build 120-volt generators. We built a big load bank in which we dissipated this 120-volt power so we could run the generators through their entire performing range. The generators worked fine until we did a critical test to learn how they worked at altitude. When the generator’s carbon brushes spark they generate plasma, and plasma is a good conductor. As we go up in altitude, we pass through the Passion-Law-Minimum where the air is at its most conductive. Down at sea level the air pressure is high and when a spark is generated it goes out. In the vacuum of space there is no way sparks can be generated. However at the Passion-Law minimum the first spark between commutator bars grows into an ionized path through which the current flows until the generator burns up. That ended the era of the 120-volt direct current generators. That project was abandoned. The next approach to 120 volt power generation was to adopt 3-phase 400 hertz AC in which the Bleed Air from Propulsion Engines drives 400 Hz AC generators.

Our airplane problem was that when a generator is coupled to an airplane’s propulsion engine or a turbine, the speed varies. The engine runs at a high speed during takeoff, at another speed during cruise, and the engine slows down as the airplane lands. Hence variable frequency AC comes out from a generator which is directly coupled to the engine. There were two choices. One was to live with the variable frequency. That choice turned out to be quite troublesome. The second choice is to drive the generator with a turbine which runs on compressed air which is bled from the engine. The turbine has a governor which controls the turbine’s air-inlet valve to keep the turbine’s speed constant. For the B-52 bomber 120-volt DC power distribution had been abandoned. Our next approach was the air turbine. However, the adopted General Electric air turbine had a problem in that it produced a frequency bump in its output which came at odd intervals, and General Electric couldn’t solve the problem. The Boeing field in Seattle became filled with B-52s which couldn’t be delivered, and finally I was invited to join an assist team to help General Electric solve the problem. Ultimately the problem was solved. The turbine drove an alternating-current generator which had been built for piston engines, so it had a damper in its shaft. When the damper got loose it allowed the generator’s rotor to “bounce” on its spring-like coupling, generating the frequency hunting. After nine months the problem was solved and these air turbines went on the B-52s.

Unfortunately an alternator-driving air-turbine manufactured by another firm had its governor and over speed sensor on the shaft. Then the turbine’s bladed wheel was attached to this shaft. On one flight the turbine wheel that drove this shaft came loose. The generator slowed down, so the governor tried to maintain the generator’s output at 400 Hz, so it opened the throttle valve wide open to get more input air. The wheel sped up until it burst and sent shrapnel in all directions. The airplane crashed. That ended the era of the bleed air turbines.

Meanwhile the so-called “Swedes” at Sundstrand developed a hydromechanical drive that contains a swash plate and pistons. This swash plate makes up the difference between the varying engine speed and the required constant alternator speed. Hydraulic power makes the alternator runs at its rated speed, producing 400 Hz power output when the engine is turning slower. The alternator is made to run slower than the engine is going fast by extracting hydraulic power. Consequently this was a very efficient drive. Most commercial airplanes today have the Sundstrand hydromechanical constant speed drives that turn the 400 Hz alternators.

A problem in early airplanes which had 400 Hz ac was that we still need DC to charge the batteries and power the electronic equipment which loved DC We could put in rectifiers to make DC out of the alternating current, but if the engines shut down we would still need AC again. Therefore little motor generator sets were used. The motor ran on DC and the generator produced AC They were called rotary inverters. Alas, being a rotating piece of machinery it lacked reliability. Therefore redundant inverters were required. They had brushes and commutators which were assemblies of complicated parts. Consequently maintenance was required because carbon brushes, commutators, and bearings wore out. Furthermore, they were expensive to build. Once the transistors were invented, a solid-state inverter became feasible, and some were built.

IEEE, Power Electronics Society; integrated circuits

Oman:

Around that time I talked about the difficulties in designing solid-state inverters with some friends on the IEEE Aerospace Power Committee. Moe Forestieri from the NASA Lewis Research Center was the chairman of that committee. I thought it would please the chairman if his committee started a new conference, so I proposed to him that we get a few engineers together to exchange ideas on how we could best make an inverter that would make AC out of DC with solid-state parts. He thought it was a good idea, so we scheduled a meeting at NASA Goddard Space Center in Maryland.

Bill Cherry was a good friend and a loyal member of the IEEE. Cherry arranged free use of an auditorium for us, so we scheduled a two-day meeting there in January 1970. Unfortunately I had a skiing accident and broke my leg the week before the meeting and couldn’t attend. They managed to have the meeting anyway, and about twenty engineers presented papers. Everybody liked the meeting and wanted to have another.

Hochfelder:

When was this?

Oman:

I believe that was in 1971. We scheduled a second meeting, and we called it the “Power Conditioning Specialists Conference.” Dan Goldmin, who later became the head of NASA, was the chairman of the next conference. He thought that the name of the conference sounded too much like plumbing so he changed the name to “Power Electronics Specialists Conference.” The Conference grew. Then it was decided to organize a Power Electronics working group within the IEEE Aerospace and Electronics Systems Society. This group grew into the Power Electronics Society, which is a huge and still growing IEEE organization today. They have about half a dozen conferences every year all over the world. The Power Electronics Specialists Conference even returns to the United States once in a while. Power Electronics Technology was one of the important contributors to the growth of aerospace. Power electronic devices are all over today’s airplanes.

A recent outstanding development in power electronics was described by Tom Williams a couple of months ago at a Power Electronics Society meeting in Seattle. He talked about a new integrated circuit which produces a sine wave which is more perfect than anybody else had been able to produce. Every 50 microseconds the computer on the circuit checks about six different parameters. It puts out pulses. It’s a pulse with a converter device. It checks on the last pulse, “How did it go? Was it the right size and the right things? Okay. How about the load? Is that like the AC we’re supposed to produce? Are we overloading anything?” and so on. Then after it checks all six parameters it says, “Okay, go ahead with another pulse.” As a result the output can be variable in frequency, voltage and current, can have limits on current, and can do anything that is required.

The integrated circuits for performing this sophisticated function will cost $2 each in quantities of a million. Suddenly we have an integrated circuit that can run an induction motor at any speed and load. If we look at an old variable speed DC motor, we see a commutater which is expensive to build and brushes that wear out. However, speed of the DC motor could be varied. The paper mills once upon a time had big motor generator sets and DC motors that varied the speed so that as the paper dried it went through rollers at different speeds. It was the same way in steel mills. They had huge DC motors that were supplied DC by generator sets turned by 3-phase AC motors.

Suddenly DC motors were no longer needed because simple low-cost induction motors could do the job with $2 circuits and a few mosfets, an electrical engineer design a control which makes an induction motor run at any speed, any torque, and accelerate or decelerate its load. Therefore it has ended the DC era.

I think of my days at Allis Chalmers manufacturing company in Milwaukee, Wisconsin where we worked on the minesweepers and many other marine applications. The minesweeper was propelled by a diesel engine which drove a DC generator. Variable DC voltage was delivered to the motor, which was coupled to the propeller by gears. Thus the ship had variable speeds, and the rotation of the propeller could be reversed. The minesweeper worked beautifully. Today that is not needed, so my skills in DC machinery are no longer in great demand.

That’s my summary of what I think were the important developments in aerospace power in the past fifty years.

Educational background

Hochfelder:

You went to Oregon State?

Oman:

Yes. Now it is called Oregon State University. It was called Oregon State College when I attended there. I graduated in the Class of 1940. I recently got an invitation to its Year 2000 Reunion. I studied electric power there. Incidentally, I also worked in journalism. I wrote articles for the Oregon State Daily Barometer and worked my way up to associate editor. I was a poor farm boy and needed help, so in my first year there I got a National Youth Administration (NYA) job stacking books in the college library. For the second year they let me work in the Electrical Laboratory where I helped assemble machines and set up demonstrations. I even helped put brackets on an airplane DC generator so that it could be demonstrated to the electric power class. They decided to publish a little bimonthly newspaper in the Electrical Engineering Department called Electric Discharge. During my third year they let me be the first Electric Discharge editor as my NYA job. Consequently I got experience in editing.

Some of the most important advice I ever got in my life was from Professor F.O. McMillan, who was head of the Electrical Engineering Department. In his last class for seniors he said, “I’m going to give you some advice. Three things.” Following that advice has had its rewards.

The first piece of advice from Professor McMillan was, “Success is never made on eight hours a day.” After I graduated, in 1940 the end of the Depression era was in sight. The General Electric job went to a student whose father was working for the company Truck Ring got a job with Westinghouse. I got a job at Allis Chalmers – primarily because there was an opening in the Advertising Department. I entered my Allis Chalmer student course in that department. Nine months later the vice president saw that marine propulsion was advancing and that it needed a lot of electric work. He ripped me out of advertising and put me on the electrical test floor. I worked on a third shift that ended at 8:00 a.m. The Advertising Department still needed me to work on the Alice Chalmers Electrical Review, so I got to work an hour of overtime every morning. This was the beginning of my moonlighting, and I’ve been moonlighting ever since as well as doing interesting things.

One of my outstanding extra jobs was serving as secretary of the Engineering Society of Milwaukee and editor of Milwaukee Engineering for which the Society paid me $25 a month. Then they bought the big old Pabst mansion and converted it into a headquarters building with meeting rooms. I approached them with this proposal, “If you will let me live in the groom’s quarters in the horse barn in back of the mansion I will forego my $25 a month salary.” They agreed, so my wife and I moved in. When my mother-in-law heard about it she said, “The very idea of my daughter, a Smith College graduate, living in a horse barn.”

Professor McMillan’s second piece of advice was, “Buy some life insurance.” Therefore I bought life insurance policies from Northwestern Mutual Life Insurance Co. A $5,000 insurance policy was typical. Today I get a bill, “Please pay $109 premium. By the way, the cash value of your policy went up another $2,000 this year.” It’s been amazing what these life insurance policies have done for such a trivial amount of money. I put in $109 today and get $2,000 back. That was good advice.

The professor’s third bit of advice was to support the American Institute of Electrical Engineers, which of course is now called the IEEE. Many, many good things came to me from the IEEE. One of the most outstanding things was my first trip to China. The Chinese needed to restart amateur radio, and a friend in IEEE activities invited me to go along. These kinds of wonderful opportunities came to me only through my contacts in the IEEE, and opportunities are still coming along. I went to China with him, and we were treated like visiting kings. We delivered lectures and got amateur radio restarted there in 1981. Amateur radio has been blooming there ever since.

Employment at Allis Chalmers and Boeing

I became the supervisor of the Marine Section of the Motor and Generator Department at Allis Chalmers during the war. We built the propulsion machinery for submarines and destroyer escort vessels. Even after the war one of the propulsion drives we built for destroyer escorts went on a Great Lakes ore carrier. I got to go on the trial run of ship. On that trip I met Charles Kettering the General Motors who invented the self-starter.

I got to meet Boss Kettering. At the end of the war, marine business collapsed. The Marine Section became just one engineer, namely me. Looking for work, I read about Boeing. I thought it would be good to work for Boeing and went for an interview. I learned that they were anxious to hire someone who understood AC machinery and could work symmetrical components. I got a job in their Acoustics Electrical Department, which turned out to be a critical experience in my life.

At that time Allis Chalmers, General Electric and Westinghouse were the big three in the electrical industry. Those three companies found that it was convenient to get together regularly in Cleveland. Important officials from those three companies met in a hotel to discuss the growing costs of labor and so on. General Electric would say something like, “Well, we’ve got to change our price books. We’re going to raise our prices by 5 percent,” and the others would say, “Okay.” Then when the others got home they’d say, “We can’t sell at a lower or higher price than General Electric, so we’ll just copy their price book and pass that out.”

Then they had a little problem about divvying up government contracts, so they came to an understanding where one company would be designated in advance to make a “mistake” and quote a price that was a little bit lower than the catalog and thereby win the contract. Sure enough, it worked. Then there were also the little companies that started cutting prices. They had to be persuaded to join the informal organization.

Hochfelder:

It sounds like a cartel.

Oman:

That’s right. The little companies demanded a portion of the output of the total year’s projects. This involved big negotiations. The government finally caught onto this activity, and some of my friends ended up in jail on antitrust violations.

These companies had not done any research on new developments. There was only one engineer in the Motor and Generator Division at Allis Chalmers working on insulation, but there was no real research. Meanwhile the Japanese and European firms were doing real research, and as soon as the cartel fell apart, these foreign firms offered new products that beat the daylights out of the existing American products. As a consequence, Westinghouse pulled out of electrical machinery, Allis Chalmers went bankrupt, and General Electric is all that’s left of the big three. The utility companies are buying imported generators, motors, transformers and substation switchgear. It was a good thing I left out of Allis Chalmers when I did.

Hochfelder:

You began working for Boeing in 1948.

Oman:

Right.

Hochfelder:

You mentioned that Boeing was looking for someone with knowledge of symmetrical components. Would you explain what is meant by symmetrical components?

Oman:

It’s a method of analyzing three-phase circuits that also carry single-phase loads. Every load on the line can have a different phase angle. Every load is converted into three mathematical components that are added to the components of the other loads which are going through the line at the same time. This analysis will produce the current in each phase of the three-phase generator and the power factor in each phase. Systematical components provide a convenient way of analyzing power lines, voltage drops, imbalances etc. This process used to require a lot of slide rule work, but today the calculations can be done very quickly with a computer.

Hochfelder:

Was that a method that very few people knew?

Oman:

No, it was used commonly in public utilities, but an engineer didn’t learn it in undergraduate studies. I did some graduate study at the Illinois Institute of Technology and was able to understand these and other subjects.

Peacekeeper and Minuteman programs

Hochfelder:

You spent roughly forty-three years in Seattle. Is that correct?

Oman:

I worked forty-three years at Boeing. Then I had an interesting option offered to me. When I was seventy-three years old I was working on the Peacekeeper and Minuteman programs. Then came the collapse of the Soviet Union, and the Cold War ended. I was in the military section of Boeing here, they had too many managers. There were desperate high-level managers in Wichita who needed jobs. They told me, “Hey, it’s time for you to retire.” They suggested that I could either transfer back into engineering or retire in management. There was the little matter of one and a half years of sick leave that I had never used, for which they would pay me half if I retired from management. However, if I went back into engineering I would lose it all. I talked to my boss about it and he said, “You’re doing something really important. Let’s get that finished first.” For about year and a half I went from one important job to another. Personnel kept saying, “Hey, you’ve got to retire,” and my manager would say, “I’ll call them up and tell them you’re needed here a little while longer.”

I worked on testing the Rail Garrison deployment of Peacekeeper ballistic missiles. The Peacekeeper went through many interesting developments. It was a brand new missile and its design was way ahead of the missiles which the Soviets had. Our older Minuteman missiles were in concrete silos. If there was a near-miss the silo would survive, and a powerful mechanism could open the cover. The missile would then be launched to avenge whomever shot the missile that damaged the surroundings. We even had interesting problems with the electromagnetic pulse from an exploding missile. This pulse run down the wires and burn up everything inside the shelter. Therefore we had to design filters that would stop this pulse. These filters were big inductors that hung on the inside wall of the silo.

It was far more difficult than a lightning arrester, because this inductor could have thousands of amperes threatening to go through it. Then there was the question of where to put the Peacekeeper missiles, because new navigation technology made near misses obsolete. If we put those missiles in a Minuteman-type shelter the Russians would learn exactly where they were located. With their modern missiles they would demolish the Peacekeepers. We had some interesting options. First were the multiple horizontal shelters. We would have 400 shelters scattered around Nevada and Utah and about forty missiles. These missiles and dummy missiles would be continually shuttled between the shelters so that the Russians wouldn’t know which shelters had the missiles and they would waste all their missiles wrecking the 400 shelters. That sounded like a good idea until some popular movement caught onto it and raised such a rumpus that this basing concept had to be abandoned.

The next Peacekeeper basing approach was deep underground tunnels where we would store missiles in tunnels 2,000 feet underground. When war started we would drill a hole to the surface and launch the missiles through this hole. This idea required underground power sources that would run for a month with no air or cooling. This was a problem because you had to have people down there that would survive. Deep underground basing turned out to be a very expensive operation. Heat sinks were also a real problem. However I got to study nuclear power plants and some alternatives. There were many problems and we worked on many solutions.

In the Rail Garrison plan, the missiles are stored on trains in military bases. When war looks imminent, the missiles move out on trains. The Russians can spot where the train is but they don’t know where it will be when their missile arrives out. Thus it’s hard to destroy those Peacekeeper missiles which are kept in Rail Garrisons. It sounded like a good solution. We built a test track at Vandenberg Air Force Base. We had a big assembly building where we were going to assemble these missiles and put them on railroad cars. However we needed power at this building, so we created a design in which we would supply power from a substation to the building through existing distribution lines by extending these lines a couple of miles. The chief civil engineer at Vandenberg said, “No, you can’t do that until you can show me that the voltage at the existing facilities will not be out of specifications when you are using power in your facility.”

That created an interesting problem. I started out by analyzing the voltage drops along the line and guessing at the loads at the stations. I spent about a week to profile one load. However we had a friend in Oregon who had developed a computer program analyzing power lines, so we got him onboard to do the computations. He figured out where we had to put the capacitor banks on the lines, so we proposed that solution. The chief civil engineer responded, “No, you’ve got to show me.” That meant we had to test the planned power line modifications. Therefore, after the capacitor banks were installed, I had to organize a test team and rent a huge load bank which simulated the building’s loads. Our friend from Oregon with his model of the line on a computer was also on that team. We ran the test and everything worked perfectly. We were able to show the chief civil engineer that all voltages at buildings along the line were within specifications, so he told us to go ahead with the project.

I had to write some reports, and as I was writing them Personnel came around again saying, “Hey, you’ve got to get rid of this guy” – meaning me. However there were Minuteman troubles because the old motor generator sets were getting old. Those engine generator sets were Alice Chalmers sets and they had to be replaced. No one else there knew how to do that, so I got to work on that problem. Someone who understood diesel generator sets was needed and modern engineers didn’t understand them.

Finally on the critical day my boss called me in his office and said, “We’re desperate. If you’re not gone this afternoon, your pay is coming out of my pay.” I had about three hours to pack up and get out of the plant. There were no farewell parties. However I had two months of vacation coming to me, so on the final date when I officially retired I was in China on a bicycle trip.

Before my bicycle trip to China the Tianamnin Square incident had occurred. Hong Kong architects had previously designed and built fine hotels in China’s cities which were fourteen to twenty stories high. To make the Japanese tourists comfortable they had installed Hitachi elevators, and to make the American tourists comfortable they had installed bathroom fixtures. Then suddenly all these hotels became empty. In an attempt to fill them again, they decided to bring to China American bicyclists. They contacted Dr. John Torosian, the president of the League of American Bicyclists. I don’t know how he got my name, but he invited me to go along, and he didn’t have to ask twice. In China, we saw all the great sights, and we were treated like royalty. In Beijing the streets were filled with bicycles, wagons and buses. We were provided a police escort with a siren blowing. Another officer on a motorcycle accompanied us with a loudspeaker: “Get out of the way and let these bicyclists through.” We were given the red carpet treatment. On my official retirement date we were eating at a fancy hotel in Shanghai, and they had a little party for me and gave me a retirement present.

Hochfelder:

That sounds good.

Oman:

There was an interesting consequence of the work we did at Vannenberg Air Force Base in planning the testing of the Rail Garrison for Peacekeeper missiles. Mike Unger, who represented Engineering Development Associates in Oregon did the computer analysis of the distribution line supplied power to the Assembly Building. After the work was done, was successful and we were able to go ahead with the Rail Garrison development, I wrote a letter for our Materiel Department to send to Engineering Development Associates saying what a wonderful job Mike Unger did. We decided that that work might make a good paper for the IEEE Power Electronics Society, so I wrote a paper. I showed Mike Unger as a co-author of this paper, and on the submittal form I needed to fill in Mike Unger’s position, so I called him to ask. He said, “Well, I’m president of the company now. Thanks for the nice letter.”

An Air Force Captain was also involved, so I wrote a letter to him saying that his contribution was important. After he retired from the Air Force, he called me and said, "I’m applying for an engineering license. Would you please tell them about the wonderful work we did at Vandenberg Air Force Base?”

Hochfelder:

Was he applying for a Professional Engineering license?

Oman:

Yes. I wrote him a good report and he got registered without any trouble. There are two Peacekeeper revelations which followed the ending of the Cold War in 1991. After we were through with Peacekeeper Rail Garrison development, we discovered that the Soviets had Rail Garrison in operation ten years before we did. Some of our satellite photographs showed this. In the early 1980s they had the Rail Garrison already in operation, whereas ours wasn’t ready for operation until around 1991. We were a little bit late, but in 1991 the Soviet Union collapsed.

Testing electromagnetic radiation emitted from transmission lines

Oman:

Another amusing sidelight in those days was the popular belief that transmission lines caused cancer because the wires produced electromagnetic radiation. In testing the distribution line, we had rented a 2-megawatt load bank which we connected to the distribution line’s end so that we could vary the load on the line. We had observers at various positions on the line who read meters to measure the line voltage. This gave the absolute proof which the base civil engineer had requested. I thought that it would be interesting to see how much electromagnetic radiation this produced. We were going to vary the current flowing through the line. Thus if we could measure the electromagnetic radiation under the line we would get some real data on its intensity.

We rented a costly magnetometer, put it underneath the line and then I took readings as the load was varied. I plotted all the readings. Then the most amazing thing that I learned was that turning the load from off to full on made very little difference in the measured electromagnetic level. Apparently the electromagnetic fields other sources such as television and FM transmitters put out more radiation than did the power line. After that I went home and did some calculation. Sure enough, the radiation from the line was substantially below even that of the earth’s magnetic field. We wrote a paper on this result and presented it at the IEEE Power Engineering Society meeting in Texas. Now other scientific data show that all this publicity of people getting injured with radiation from power lines is false. Someone developed that fallacy to create an issue where there really wasn’t one. The era of presenting papers on electromagnetic radiation from power lines is over. I had just happened to be available at the right time with the right data.

Airplane power work at Boeing

Hochfelder:

Let’s talk about your early career at Boeing after you arrived there in 1948. Would you talk about some of your technical achievements from then until now?

Oman:

During the early part of my career I worked on airplane power. An amusing incident occurred during one of my first projects. There was a problem of the fuses – then called limiters – which would clear a faulted line. Their characteristics were not very well understood, particularly what would be the current pulse through the fuse as its resistance changed during blowing. Therefore I worked on a project in which we analyzed the burning limiter and measured its changing voltage drop with an oscilloscope. The analysis involved modeling the limiter’s varying resistance. As the limiter got hotter its resistance increased. All metals and resistors perform that way. Hence there would be a growing voltage drop across the limiter as it carries fault current. Therefore once it gets hot it goes on to melting temperature quickly. Then the limiter has to clear enough trash metal out of the way so it can interrupt the circuit.

While doing the analysis I tried to analyze point-by-point how that resistance varied. In those days we had women that served as engineers’ assistants at non-professional pay. One assistant had studied a lot of mathematics. I had written a paper on the study and needed to write a derivation, so I created the derivation and asked this assistant to check it. She came back and said, “Look, here’s a formula that will do it. Why don’t you just use the formula?” Sure enough, she was right. Eventually she became a vice president of Boeing in charge of the computer programs.

Hochfelder:

Really?

Oman:

She had a lot of brains behind her. Anyway, I used that material and got the equivalent of a Master’s degree, which they then called a Professional Electrical Engineer degree at Oregon State. After that I worked on the B-52 bombers and airplanes. Then came the atomic-powered airplane. It had a reactor which produced heat to power an air turbine. Power was generated by a smaller turbine which drove the generator. The reactor eas at the end of a boom which extended rearward from the tail of the airplane. A shadow shield at the front end of the reactor was necessary for shielding the crew from reactor radiation. Figuring out whether it was better to put the generator at the hot or cold end of the shadow shield is an example of the kind of studies we made. That project was a lot of fun. I got to visit Oak Ridge where I saw the reactor that was suspended on a cable high up in the sky to simulate the airplane type of operation. I also got to see many other facilities.

There is a new book written by Stewart Udall, The Myths of August: A Personal Exploration of Our Tragic Cold War Affair with the Atom. Among the things it says is that the nuclear powered airplane is about the dumbest idea that was ever pursued.

Hochfelder:

Do you agree or disagree with that?

Oman:

It was a wonderful opportunity for me. I got to visit all these nuclear power plants and even got to go into the one at Hanford where they made plutonium. We also got to read classified reports, which provided me a lot of education. The Atomic Energy Commission, in order to run the necessary tests, acquired an area in Idaho which was as big as the State of Rhode Island. In their testing, they finally got an air turbine to run on heat from a nuclear reactor. They got the reactor out of the underground test chamber, and managed to run the air turbine that the shielded reactor produced. However, no airplane could lift the shielded reactor into the air and there was no way that it could be useful in a military airplane. The reactor was so heavy that the huge airplane which carried it would have had to fly at subsonic speeds. The atomic scientists assembled at a big meeting where they were discussing the report on their progress. Then a message came from Washington, DC: “Cancel the meeting. We’re all through.”

Stewart Udall had criticized our proposed deployment of Peacekeeper missiles in the desert as the most harebrained scheme proposed by the Pentagon. He also said that the development of the nuclear powered airplane was a waste of money.

Battery work at Boeing; forming Electric Bicycle Company

That’s a hard question to answer because there were so many, and they were interelated. Once in my early days at Boeing, I was working very seriously on batteries. In fact, I was designated as the company battery expert. That lasted about a year before they put me on another project. Later on when we got into the Peacekeeper missile and spacecraft work, battery expertise was needed again, and I developed a lot of expertise on batteries. When I retired I had just returned from a battery conference. Another engineer who had also retired and asked me which batteries were the best and most current. He was working on battery-powered electric bicycles. We got together and formed the Electric Bicycle Company. We built dozens of prototype electric bicycles. We ran them for long distances over varying topographics and measured their energy consumption. A paper I presented last summer was on the topic of the cost of traveling 1,000 miles. I had previously presented a paper on the cost of travel comparing everything from the Queen Mary steamship to walking, bicycling, and putting on a dolphin suit and swimming in the ocean. The dolphin suit provided the lowest energy consumption possible. No energy is needed to keep afloat and all one has to do is swim. The dolphin suit is very streamlined. There’s a turbulent water flow and a laminar water flow. When a vehicle traveling in water exceeds a critical speed it generates turbulent flow and the propulsion power consumption goes up. During the 1920s when there were passenger-carrying steamships, dolphins would swim around the bows of those ships which were traveling at 25 knots. People were puzzled. Engineers worked on the problem. “How can a dolphin go so fast?” A scientist developed equations showing that in traveling at the high speed the dolphin’s muscles delivered four times the energy that any known muscle is able to produce. This became known as Smith’s Paradox. Then dolphin pools were built in the eastern states. For $50 one could listen to a lecture on dolphins and go into the pool and swim with the dolphins. The things the lecturer says is, “The dolphin will swim to you and stick his tongue out. You then pat the dolphin’s tongue. Then you become friends and you start playing. You throw the dolphin, the dolphin throws you,” and so on.

There it was discovered the dolphin’s skin vibrates! Subsequent analysis showed that the vibrating skin is able to go through water with laminar flow, even at speeds above turbulent-flow speeds. Thus dolphins have the most efficient propulsion system. If one swims in a dolphin suit and vibrates the surface of the suit, then the energy equivalent of one gallon of gasoline would drive that person 3,000 miles.

The electric bicycle turned out to be too expensive. A series of glider hoisting stations placed fifty miles apart. Cheaper fuel consumption could be obtained by captive balloons that are connected by a girder that supports a cable. A glider, after being lifted to 50,000 feet with that cable, glides for fifty miles, then gets hoisted up again at the next station. The diesel fuel consumed in raising the glider to 50,000 feet corresponds to about $4 per thousand miles of glider travel. A bicycle consumes less energy, but you have to eat cheese to get it. That costs about $8 per thousand miles. However, with an electric bicycle using 2¢ per kilowatt hour of electricity, the travel energy falls to $2 per thousand miles, so electric bicycles beats the other energy sources in cost for traveling a thousand miles.

Hochfelder:

Except for the dolphin suit.

Oman:

Yes, and incidentally, that paper that discusses the cost of traveling a thousand miles was one of the key papers that got me an award in our IEEE Aerospace and Electrical Systems Magazine. I wrote that paper in 1988, and for that I was presented the Harry Mimno Award. Last summer at the Intersociety Society Energy Conversion Engineering Conference I gave a corrected number, which is $2.80 per thousand miles for electric bicycles.

Solar power research

Oman:

I forgot to tell you about solar power. Once spacecraft started flying, I got into solar power, and we did a lot of research on solar-cell panels. Two of our engineers even patented a V-ridge panel on which the direct sunlight arriving on a string of solar cells is supplemented by sunlight reflected from a sloping surface of aluminum on each side of each solar-cell string. Then I worked on a solar power satellite, which when in geosynchronous orbit, would generate the power equivalent of ten nuclear power plants. This power would be delivered down to earth via a microwave beam. Last year I was invited to write a paper for a conference in Moscow, organized by the Russians. They have been working on solar power satellites. We had stopped our work about ten years ago because of the very high cost of boosting this satellite up into geosynchronous orbit. However, the price of hoisting satellites into orbit is expected to drop by a factor of a hundred when reusable launch vehicles become available. Therefore a solar power satellite can become practical, and we are seeing a lot of papers on the subject. The Russians had a conference last summer at which four papers on solar power satellites were presented. I didn’t have the funds to go there, so they had someone present my paper for me. Those are some of the exciting things I did at Boeing.

Thirty-eight years ago the oil embargo created a problem, and power became a critical element. The oil embargo shut off oil, and cars lined up at filling stations trying to buy gasoline. This produced a surge of interest in power and alternative ways of generating it. Many challenges such as the problems in producing wind and solar power, hydropower, energy storage and pumped hydro storage. We had a sparsely-attended IEEE energy conference, as did the other societies. Then it was decided to have one conference where everyone could get together to discuss energy problems and development. I represented the Aerospace Electronic Systems Society at the meeting, where we decided to start the Intersociety Energy Conversion Engineering Conference (IECEC). The engineering societies took turns running this conference, and eventually seven engineering societies participated. Every seventh year the IEEE Electronics Society and the Aerospace and Electronics Systems Society ran this conference. We’ve been doing that for the past thirty-five years.

I was at the first (IECEC), which was held in Los Angeles at a hotel near the airport. Outside that hotel and during the meeting, workers were cutting up the street for some reason. In the middle of a session, they accidentally cut through the power line supplying the hotel. It was a really hot day. We had no air conditioning and no power for the chart projector or amplifier. If we opened the windows the roaring noise of jackhammers came in, so we had to keep the windows closed. We ran the conference for about three hours with no power. That was an ironic setting for our first IECEC. I’ve been associated with the conference ever since. I still go to every IECEC, where I plead for free registration so that I can write reports on the conferences for IEEE AES Magazine.

Hochfelder:

That sounds good.

Oman:

There’s another magazine, Advanced Battery Technology, which is run by a guy who is non-electrical and publishes several magazines. His wife is the managing editor of Advanced Battery Technology. I supported its predecessor magazine with a report on each IEEE Annual Battery Conference. When he and his wife took over the magazine she invited me to write Battery Conference reports for them. I said, “Sure.” Then came the Hawaiian Battery Conference, which this couple attended. She found that it was stressful sitting in this conference listening to papers so she decided to go out on the beach and relax. I got a desperate message from her: “Would you write us an article on this Hawaiian Battery Conference? We’ll overnight the Proceedings to you.” I accepted and I wrote for them a big article. I got lots of pictures, filled many column inches in her magazine, and received a beautiful check for my work. A related incident occurred when a magazine dealing with standards had asked a guy from Quebec Hydro to write an article about the battery standards reported at the Hawaii conference. He was too busy, so they came to me and asked, “Will you please write an article on lithium batteries?” I wrote that article for them, and it was recently published. I get a lot of invitations to write articles.

Predictions for power electronics and aerospace systems

Hochfelder:

Would you describe what you think some of the technical challenges will be for engineers in power electronics and aerospace systems in the next ten to twenty years?

Oman:

A very important challenge will be to get rid of the nasty hydraulics on airplanes. Looking at the military picture, when they move an Air Force squadron to someplace like the Middle East, they need a whole fleet of cargo airplanes to bring the apparatus for keeping the hydraulics going. They must also bring planeloads of spare parts. Then they don’t always have on hand the right spare parts. It’s a real mess. In commercial airplanes the hydraulics leak and the hydraulic fluid flows on the walls and on the floor. Additionally, hydraulics equipment is expensive and requires a lot of pipes that must be carried on airplanes.

Today we can build electric actuators, linear actuators and motor actuators. We now have inverters that -- with a $2 control -- will make a motor drive do almost anything. The motors for actuators can be variable speed induction motors which don’t have commutators or brushes. The electric actuator is a key development, and will go into all kinds of airplanes. The next important development will be replacing other hydraulic actuators with electric actuators. That development will probably spread into all industries. For example, across the street from my home they are building a new house. There is a crane that is about 100 feet high and it has a big hydraulic hose through which concrete cement is pumped. There is a tremendous opportunity for replacing hydraulics with electric actuators.

Another thing that we no longer need is constant frequency AC, which we can make very easily now. The new airplane engines will have on the jet engine’s shaft a rotor that will carry permanent magnets. Around the magnets there will be coils that will generate variable frequency alternating current. There will be no brushes or commutators on the rotating shaft. There will be no gears, clutches or hydraulics to worry about. The coils generate alternating current which varies in voltage and frequency as the speed of the jet engine’s rotor varies. However, this will no longer be a problem. The electric power goes into the magic box and out comes whatever voltage and frequency is needed.

Then there is now an incentive to use DC instead of AC distribution. We abandoned DC distribution because the DC generator’s brushes and commutator would flash over in high altitudes. However we don’t need commutaters and brushes anymore, so DC distribution is a coming thing. We will have the high voltage, and we now have high voltage transistors. Also, the voltages of the mosfets are going up. The mosfets are beautiful. They have milliohms of resistance, so their housing doesn’t even need to be cooled since little heat is generated in it. I think those are the key upcoming developments in aerospace electronics.

We also need power in satellites and spacecraft. I think a key development will be the solar power satellite that operates in synchronous orbit. We showed before that if we could get the cost of launching down to one-tenth of today’s launch cost, the solar power satellite could be economically practical. Its delivered power would be cheaper than power generated by burning oil. The cost of launching cargo into earth orbit is going to fall to one tenth of todays cost. That is looking pretty good, and opportunities are there. There is an American firm that is proposing to generate power with solar cells on a huge solar array on a space station in geosynchronous orbit, immediately converting the DC power to radio frequency AC power, and send it through a coaxial cable to the microwave transmitter. The transmitter has a huge antenna and requires a high-voltage input. If the power is received at radio frequency the transformer will be very light in weight. Power sent at 400 hertz would require tons of transformer.

Hochfelder:

Right.

Oman:

There is a science need to see find out what the solar corona is like. The solar corona is very hot, and if you go close to it everything melts. Therefore the solar-corona exploring spacecraft has to have a shield on it which reflects sunlight in order to keep the spacecraft cool. To generate power, a little hole is made in the shield to admit a beam of light which is absorbed in a tungsten can that has a radiating outer surface. Solar cells inside a surrounding drum convert the light radiated by the can to electric power.

Hochfelder:

That is a pretty new technology, isn’t it?

Oman:

Yes. There is an interesting new development in converting heat to electricity. Engines are limited in efficiency by the Carnot cycle, meaning that more heat cannot be gotten out of a hot surface. The maximum engine efficiency is the difference between source and sink temperature, divided by the source temperature in absolute units. With any source and sink temperature difference, there is a certain amount of energy, but with an engine only part of this energy can be recovered.

Hochfelder:

Right.

Oman:

However an electronic converter doesn’t have to obey the Carnot-cycle efficiency limit. We now have a new battery-like device that converts heat into electricity and has efficiencies up to 20 percent. They can’t compete with high temperature heat engines, but they beat thermoelectric converters that are only 3 to 4 percent efficient. Thermoelectric converters now power our spacecraft in deep space missions. There are lots of exciting things coming up.

Advice to young engineers

Hochfelder:

Do you have any final thoughts with which you would like to conclude?

Oman:

My final thought would be for young engineers: Pay attention to advice you get, because there is some good advice available. I cite my example of advice that Professor McMillan gave to our 1940 senior electrical engineering class at Oregon State College. You can no longer support the American Institute of Electrical Engineers because it’s gone, but you can support the IEEE. That’s an important thing to do. He told us that success is not made on working only eight hours a day. He told us to buy life insurance, and there are still some opportunities for insurance investments.